<?php
function isDate($date){
	//formato valido "28/02/2009";
	$char = strpos($date, "/")!==false?"/":"-";
	$date_array = explode($char,$date);
	if(count($date_array)!=3) return false;
	return checkdate($date_array[1],$date_array[0],$date_array[2])?($date_array[2] . "-" . $date_array[1] . "-" . $date_array[0]):false;
}

if($date_ckecked=isDate($date)){
	return true;
}else{
	return false;
}